well, it's a big topic :)

1. CGI is about faking things, so you have know what you want to fake.

2. Fake, fake, cheat and fake! ;) You're trying to make a nice image, realism may, or may not be a factor. But it's not like making a photograph, you can cheat to achieve what you wish.

Example, pic I did today, I didn't need to show the ground, it would just get the way of what I had arranged, all I did was lift the character and platform she stood on, up a few feet in the air, so, the angle of the camera would then not show the ground! Simple ;)

Lots of tricks like that you learn over time, you don't become good in days...

Another trick: I wanted thick mist in the trees, easy, just use a metacloud, drop it into the trees, scale the cloud objects, and alter material to make a nice mist.

Also, with Spectral atmospheres, go to "Sky Fog and Haze" tab
See the quality boost Slider ? when doing your final render,once it's all ok, turn that up to the maximum, makes clouds much nice looking.

Edit all lights, turn shadows to about 85%, to stop shadows being to harsh and solid. Make the lights "soft", varying between 1(harsh strong light)  and 10 degrees (candles, camp fire etc), note that does increase render time, and you need to edit the light and increase the quality of the softness to +1 or more to remove noise from the shadows.

As folk note, check Geekatplay and my site for tutorials, Peggy's course, and the "Vue 6 Revealed" book by Richard Schrand..and realize it takes time to be a good artist...
10% inspiration, 90% persperation ;)

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